The invention relates to an olefin polymer of high molecular weight and low residual catalyst content.
Isotactic PP is prepared with the aid of ethylene-bis-(4,5,6,7)-tetrahydro-1-indenyl)-zirconium dichloride together with an aluminoxane in a suspension polymerization reaction (cf. EP-A-185,918). The polymer has a narrow molecular weight distribution (Mw/Mn1.6 to 2.6).
It has been possible to achieve a considerable increase in the activity of the catalyst system by a specific preactivation method (cf. DE-3,726,067). The particle morphology of the polymer has likewise been improved by this preactivation method.
The molecular weights of the polymers obtained in accordance with these two applications are still too low for industrial use.
There was thus the object of discovering a process for the preparation of a high molecular weight olefin polymer which can be carried out in an industrially interesting temperature range with a high catalyst activity.
It has been found that the object can be achieved by polymerization of olefins in the presence of certain metallocene catalysts.
The invention thus relates to a process for the preparation of a polyolefin by polymerization of an olefin of the formula R11xe2x80x94CHxe2x95x90CHxe2x80x94R12, in which R11 and R12 are identical or different and are a hydrogen atom or a C1-C14-alkyl radical, or R11 and R12, together with the carbon atom joining them, form a ring having 4 to 28 carbon atoms, at a temperature of 0xc2x0 C. to 150xc2x0 C., under a pressure of 0.5 to 100 bar, in solution, in suspension or in the gas phase and in the presence of a catalyst which consists of a metallocene and an aluminoxane of the formula (II) 
for the linear type, and/or of the formula (III) 
for the cyclic type, in which, in the formulae (II) and (III), R10 is a C1-C6-alkyl group and n is an integer from 2 to 50, wherein the metallocene is at least one compound of the formula (I) 
in which
M is zirconium or hafnium,
R1 and R2 are identical or different and are a hydrogen atom, a C1-C10-alkyl group, a C1-C10-alkoxy group, a C6-C10-aryl group, a C6-C10-aryloxy group, a C2-C10-alkenyl group, a C7-C40-arylalkyl group, a C7-C40-alkylaryl group, a C8-C40-arylalkenyl group or a halogen atom,
R3 and R4 are identical or different and are a hydrogen atom, a halogen atom, a C1-C10-alkyl group or a xe2x80x94NR29, xe2x80x94SR9, xe2x80x94OR9, xe2x80x94OSiR39, xe2x80x94SiR39 or xe2x80x94PR29 radical, in which R9 is a C1-C10-alkyl group, a C6-C10-aryl group or, in the case of radicals containing Si or P, also a halogen atom,
or in each case two adjacent radicals R3 or R4, together with the carbon atoms joining them, form a ring and
R5, R6, R7 and R8 are identical or different and are a hydrogen atom, a halogen atom, a C1-C30-alkyl group, a C1-C10-fluoroalkyl group, a C6-C10-aryl group, a C6-C10-fluoroaryl group, a C1-C10-alkoxy group, a C2-C10-alkenyl group, a C7-C40-arylalkyl group, a C8-C40-arylalkenyl group, a xe2x80x94SiMe3 group, an xe2x80x94OSiMe3 group or a C7-C40-alkylaryl group, or R5 and R6 or R7 and R9, in each case together with the atoms joining them, form a ring.
The catalyst to be used for the process according to the invention consists of an aluminoxane and at least one metallocene of the formula I 
in which
M is hafnium or zirconium, preferably zirconium,
R1 and R2 are identical or different and are a hydrogen atom, a C1-C10-, preferably C1-C3-alkyl group, a C1-C10-, preferably C1-C3-alkoxy group, a C6-C10-, preferably C6-C8-aryl group, a C6-C10-, preferably C6-C8-aryloxy group, a C2-C10-, preferably C2-C4-alkenyl group, a C7-C40-, preferably C7-C10-arylalkyl group, a C7-C40-, preferably C7-C12-alkylaryl group, a C8-C40-, preferably C8-C12-arylalkenyl group or a halogen atom, preferably chlorine.
R3 and R4 are identical or different and are a hydrogen atom, a halogen atom, preferably a fluorine, chlorine or bromine atom, a C1-C10-, preferably C1-C3-alkyl group or a xe2x80x94NR29, xe2x80x94SR9, xe2x80x94OR9, xe2x80x94OSiR39, xe2x80x94SiR39 or xe2x80x94PR29 radical, in which R9 is a C1-C10-, preferably C1-C3-alkyl group or C6-C10-, preferably C6-C8-aryl group, or in the case of radicals containing Si or P also a halogen atom, preferably a chlorine atom, or two adjacent radicals R3 or R4, together with the carbon atoms joining them, form,a ring. Particularly preferred ligands are indenyl, fluorenyl and cyclopentadienyl.
R5, R6, R7 and R8 are identical or different and are a hydrogen atom, a halogen atom, a C1-C30-, preferably C1-C4-alkyl group, in particular a methyl group or ethyl group, a C1-C10-fluoroalkyl group, preferably a CF3 group, a C6-C10-fluoroaryl group, preferably a pentafluorophenyl group, a C6-C19-, preferably C6-C8-aryl group, in particular xe2x80x94CH2xe2x80x94C6H5 or xe2x80x94C6H5, a C1-C10-, preferably C1-C4-alkoxy group, in particular a methoxy group, a C2-C10-, preferably C2-C4-alkenyl group, a C7-C40-, preferably C7-C10-arylalkyl group, a C8-C40-, preferably C8-C12-arylalkenyl group or a C7-C40-, preferably C7-C12-alkylaryl group, or R5 and R6 or R7 and R8, in each case together with the atoms joining them, form a ring.
Especially preferably, R5, R6 and R7 are a hydrogen atom and R8 is a phenyl, benzyl, methyl, ethyl, trifluoromethyl or methoxy group, or R5 and R7 are a hydrogen atom and R6 and R8 are a phenyl, benzyl, ethyl, methyl, trifluoromethyl or methoxy group.
The metallocenes described above can be prepared in accordance with the following general equation: 
(X=Cl, Br, J, O-Tosyl, HRa=
HRb=
The cocatalyst is an aluminoxane of the formula II 
for the linear type, and/or of the formula (III) 
for the cyclic type. In these formulae, R10 is a C1-C6-alkyl group, preferably methyl, ethyl or isobutyl, in particular methyl, and n is an integer from 2 to 50, preferably 5 to 40. However, the exact structure of the aluminoxane is not known.
The aluminoxane can be prepared in various ways.
One possibility is careful addition of water to a dilute solution of an aluminum trialkyl by introducing the solution of the aluminum trialkyl, preferably aluminum trimethyl, and the water, in each case in small portions, into a larger amount of an inert solvent initially introduced into the vessel, and awaiting the end of the evolution of gas between each addition.
In another process, finely powdered copper sulfate pentahydrate is suspended in toluene and, in a glass flask under an inert gas at about xe2x88x9220xc2x0 C., aluminum trialkyl is added in an amount so that about 1 mol of CuSO4. 5H2O is available for every 4 Al atoms. After slow hydrolysis, alkane being split off, the reaction mixture is left at room temperature for 24 to 48 hours, during which it must be cooled if appropriate, so that the temperature does not rise above 30xc2x0 C. The aluminoxane dissolved in the toluene is then filtered off from the copper sulfate and the solution is concentrated in vacuo. It is assumed that in this preparation process the low molecular weight aluminoxanes condense to form higher oligomers, aluminum trialkyl being split off.
Aluminoxanes are furthermore obtained when aluminum trialkyl, preferably aluminum trimethyl, dissolved in an inert aliphatic or aromatic solvent, preferably heptane or toluene, is reacted with aluminum salts containing water of crystallization, preferably aluminum sulfate, at a temperature of xe2x88x9220 to 100xc2x0 C. In this procedure, the volume ratio between the solvent and the aluminum trialkyl used is 1:1 to 50:1xe2x80x94preferably 5:1xe2x80x94and the reaction time, which can be monitored by the splitting off of the alkane, is 1 to 200 hoursxe2x80x94preferably 10 to 40 hours.
Of the aluminum salts which contain water of crystallization, those which have a high content of water of crystallization are used in particular. Aluminum sulfate hydrate, especially the compounds Al2(SO4)3. 16H2O and Al2(SO4)3. 18H2O with the particularly high water of crystallization content of 16 and, respectively, 18 mol of H2O/mol of A2(SO4 )3, is particularly preferred.
Another variant for the preparation of aluminoxanes comprises dissolving an aluminum trialkyl, preferably aluminum trimethyl, in the suspending agent which has been initially introduced into the polymerization kettle, preferably in the liquid monomer or in heptane or toluene, and then reacting the aluminum compound with water.
In addition to the processes described above for the preparation of aluminoxanes, there are others which can be used.
Regardless of the nature of the preparation, all the aluminoxane solutions have a common feature of a varying content of unreacted aluminum trialkyl which is present in the free form or as an adduct.
It is possible to preactivate the metallocene with an aluminoxane of the formula (II) and/or (III) before use in the polymerization reaction. The polymerization activity is in this way significantly increased and the particle morphology is improved.
The preactivation of the transition metal compound is carried out in solution. Preferably, in this procedure, the metallocene is dissolved in a solution of the aluminoxane in an inert hydrocarbon. An aliphatic or aromatic hydrocarbon is suitable as the inert hydrocarbon. Toluene is preferably used.
The concentration of the aluminoxane in the solution is in the range from about 1% by weight to the saturation limit, preferably 5 to 30% by weight, in each case based on the total solution. The metallocene can be used in the same concentration, but it is preferably used in an amount of 10xe2x88x924xe2x88x921 mol per mol of aluminoxane. The preactivation time is 5 minutes to 60 hours, preferably 5 to 60 minutes. The preactivation is carried out at a temperature of xe2x88x9278xc2x0 C. to 100xc2x0 C., preferably 0 to 70xc2x0 C.
The polymerization is carried out in a known manner in solution, in suspension or in the gas phase, continuously or discontinuously, in one or more stages at a temperature of 0 to 150xc2x0 C., preferably 30 to 80xc2x0 C. Olefins of the formula R11xe2x80x94CHxe2x95x90CHxe2x80x94R12 are polymerized. In this formula, R11 and R12 are identical or different and are a hydrogen atom or an alkyl radical having 1 to 28 carbon atoms. However, R11 and R2, together with the carbon atoms joining them, can also form a ring having 4 to 28 carbon atoms. Examples of such olefins are ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, norbornene, norbornadiene, pentene, hexene or octene. Propylene is polymerized in particular.
Hydrogen is added as a molecular weight regulator if necessary. The total pressure in the polymerization system is 0.5 to 100 bar. The polymerization is preferably carried out in the pressure range from 5 to 64 bar, which is of particular interest industrially.
The metallocene compound is used in the polymerization in a concentration, based on the transition metal, of 10xe2x88x923 to 10xe2x88x927, preferably 10xe2x88x924 to 10xe2x88x926 mol of transition metal per dm3 of solvent or per dm3 of reactor volume. The aluminoxane is used in a concentration of 10xe2x88x925 to 10xe2x88x921 mol, preferably 10xe2x88x924 to 10xe2x88x922 mol per dm3 of solvent or per dm3 of reactor volume. However, in principle higher concentrations are also possible. At least one compound of the formula I is used as the metallocene. Mixtures of several compounds of the formula I or mixtures of isomers are also possible.
If the polymerization is carried out as suspension or solution polymerization, an inert solvent which is customary for the Ziegler low pressure process is used. For example, the polymerization is carried out in an aliphatic or cycloaliphatic hydrocarbon; examples of these which may be mentioned are butane, pentane, hexane, heptane, isooctane, cyclohexane and methylcyclohexane.
A benzine or hydrogenated diesel oil fraction can furthermore be used. Toluene can also be used. The polymerization is preferably carried out in the liquid monomer.
If inert solvents are used, the monomers are metered in as a gas or in liquid form.
If only one monomer is used as the suspending agent, the comonomer or the comonomers is or are metered in as a gas or in liquid form.
It is furthermore possible to carry out the polymerization in a mixture of different monomers as the suspending agent; another monomer can then be metered in as a liquid or in gaseous form. If ethylene is used, it is advantageous for some of the ethylene to be initially introduced and for the remainder to be metered in during the polymerization.
The duration of the polymerization can be as desired, since the catalyst system to be used according to the invention shows only a slight time-related drop in polymerization activity.
The process according to the invention is distinguished by the fact that the metallocenes used are very heat-stable, so that they can be used with high activity even at temperatures up to 90xc2x0 C. The aluminoxanes used as cocatalysts can moreover be added in lower concentrations than previously. Finally, it is now possible to prepare random copolymers at temperatures of industrial interest.
The metallocenes or metallocene mixtures to be used according to the invention contain compounds which can polymerize propylene to give polymers having a molecular weight of more than 150,000 g/mol, preferably 200,000 g/mol. This is confirmed by the molecular weight distribution, which has a high Mw/Mn ratio ( greater than 2). The molecular weight distribution is sometimes multimodal.
A mixture of 68.64 g (336 mmol) of methylphenyl-benzofulvene, 4.92 cm3 (61 mmol) Of CCl4 and 100 cm3 of tetrahydrofuran was added to 8.17 g (336 mmol) of magnesium filings in the course of 0.5 hour. The reaction mixture, which was warm because of the reaction which occurred, was then stirred overnight. The resulting Grignard mixture was added to ethereal HCl, and water was then added. The organic phase was separated off, dried over Na2SO4, filtered and evaporated.
The crude product was purified by column chromatography (50xc3x97250 mm; 60xc3x85, 70-200 xcexcm, starting with pure n-hexane with an increasing H2CCl2 content).
Yield 3.1 g (7.55 mmol, 4.5%), rF=0.26 (3 volumes of hexane/1 volume of H2CCl2), melting point 225-230xc2x0 C.